The objective of this project is to develop rapid and reproducible immunological and immunochemical techniques which will enable us to identify structural variants in the major histocompatibility (MHC) antigens of lymphocytes in the blood of individuals exposed to mutagenic agents. Preliminary objectives include developing a mouse animal model in which the mouse major histocompatibility antigens (H-2) may be quantitated for structural variants after exposure of lymphocytes to known or suspected mutagenic agents in vivo or in vitro and compared with the spontaneous mutation rate at these loci. Use will be made of such recent immunological advances as monoclonal antibodies against defined determinants of the MHC and the technology of rapid-flow cytometry using the fluorescence-activated cell sorter to rapidly identify and quantitate spontaneous or induced mutations at the MHC loci.